This invention relates to a linear motor-actuated flow control valve assembly having an electromagnetically actuated and controlled moving-coil linear motor, and valve means for controlling the degree of communication between an inlet port and outlet port in accordance with the operation of the linear motor. More particularly, the invention relates to a valve assembly of the type described in which the flow rate between the two ports can be controlled in proportion to the electric current applied.
In general, a linear motor-actuated flow control valve of the aforementioned type includes a moving-coil linear motor which is arranged within a casing having an inlet port and outlet port. The moving-coil linear motor comprises a hollow, ferromagnetic core which delimits valve chambers and which is provided with a valve hole for communicating the two ports, a bobbin, having an electromagnetic coil wound thereon, slidably disposed on the core for controlling the opening degree of the valve hole, permanent magnets so arranged as to produce a magnetic flux axially of the electromagnetic coil, and a ferromagnetic body for forming, together with the core, a magnetic circuit for the permanent magnets. The arrangement is such that passing an energizing current through the electromagnetic coil causes the bobbin to regulate the opening of the valve hole by moving the bobbin against a biasing force applied to the bobbin by spring means.
In the conventional linear motor-actuated flow control valve of the above kind, the bobbin is biased in a given direction (ordinarily the fully-closed direction) by the spring means. By passing an energizing current through the electromagnetic coil, a repulsive force is produced to drive the bobbin against the biasing force applied by the spring means, whereby the valve hole may be regulated to a predetermined opening degree between the fully-closed and fully-open positions as a function of the magnitude of the energizing current. One example of the relationship between the current i and the flow rate Q in such case is illustrated in FIG. 4, which shows the flow rate characteristic of a proportional relation. This type of linear motor-actuated flow control valve is frequently employed to control the air-fuel ratio in the internal combustion engine of an automotive vehicle. In such case the flow control valve operates with the valve hole open approximately mid-way while the vehicle is travelling, with control being effected either toward the fully-open or fully-closed positions from the mid-way position. Accordingly, it has been necessary to hold the excitation current at a fixed magnitude constantly under predetermined control conditions while the vehicle is running, also to apply allowable maximum current in order to open the valve hole fully when so desired. Moreover, in order to achieve stable control characteristics despite the vibration which acts upon the system, conventional practice has been to employ spring means having a considerably large spring modulus for the purpose of biasing the bobbin, and this has in turn required that the elctromagnetic coil be energized to a greater degree to be able to drive the bobbin against the force of the spring means. This makes it difficult to achieve a low level of power consumption because regulating the valve when the vehicle is running requires the expenditure of considerable excitation current.
The following is counted as additional disadvantage in the prior art:
The above-described control valve which is normally biased closed during non-excitation of the electromagnetic coil is employed as an air-fuel ratio control valve in the carburetor by-pass of a vehicle engine during engine idling. However, this can lead to a problem wherein engine starting cannot be achieved when ice forms adjacent the throttle valve of the carburetor in a cold environment since ice forms at the control valve closed.
Therefore, there has been much to be desired in the prior art.